Device and method for dosing and transporting dry urea, especially during the implementation of the scr method in motor vehicles

ABSTRACT

In a device for dosing and transporting dry urea, e.g., for implementing the SCR method in a motor vehicle, the device includes a storage vessel containing the dry urea in the form of pellets, the wall of the storage vessel having an opening to which a transport line is connected on the outer side. The device also includes a compressed air nozzle which is arranged inside the storage vessel at a distance from the opening, is oriented towards the opening, and may be supplied with compressed air, and a portioning element having an upper side oriented towards the inside of the storage vessel and a lower side opposite the wall of the storage vessel. At least one continuous channel having a larger cross section than the dimensions of the pellets connects the upper side and the lower side in order to form at least one receiving element for the pellets.

FIELD OF THE INVENTION

The present invention relates to a device and a method for dosing andtransporting dry urea.

BACKGROUND INFORMATION

A large increase in population, increased industrialization and risingamounts of traffic lead to a concentration of contaminants in theenvironmental air that has assumed critical proportions. In thisconnection, nitrogen oxide emissions are of special importance, andthese may be attributed in large measure to the combustion of gasolinefuels and Diesel fuels in automobiles. Nitrogen oxide emissionscontribute, among other things, to increased ozone concentrations atground level.

In order to counter this critical development, and based on repeatedtightening of contaminant limiting values by lawmakers, automobilemanufacturers have constantly made efforts to decrease nitrogen oxideconcentrations that are created during the operation of a motor vehicle.In this context, a possibility is the application of the SCR method,used in industrial installations, in which ammonia is added to theexhaust gas stream. In this context, the ammonia reacts with thenitrogen oxides to form nitrogen, carbon dioxide and water.

Because of the danger potential relating to the ammonia, carryingammonia along in a motor vehicle may be problematic. Therefore, it maybe possible to produce ammonia, in a quantity exactly required for thechemical reaction, from urea.

This possibility is described, for example, in German Published PatentApplication No. 40 38 054, in which an aqueous urea solution is carriedalong in a container in the motor vehicle, and, with the aid of ahydrolysis catalyst, is split into ammonia and carbon dioxide. Inpractice, however, various problems come about from the use of anaqueous urea solution. Carrying along aqueous urea not only assumes acorresponding space availability for the tank required for this, butalso increases the overall weight of the motor vehicle. Additionaldisadvantages come about with reference to the wintertime suitability ofa vehicle, because of the relatively high freezing point of the ureasolution. Besides, in the operation of the motor vehicle, the waterproportion of the urea solution has to be evaporated, so that thisenergy is no longer available to increase the reaction temperature.Also, the production of aqueous urea solutions is expensive, since theyare made using deionized water so as to avoid deposits.

The use of dry urea for producing ammonia has been considered, which,after it has been brought to a powdery consistency, is transported tothe place of application using a carrier air stream. However, theassumption for this is that the urea is in a free-flowing condition.However, this property is greatly impaired if the dry urea is exposed tomoisture, high temperatures or mechanical pressure, since then thebaking together of the urea particles may occur. Additional problemscome about while transporting solid substances by their inclination toform bridges, which may later cause clogging.

For example, European Published Patent Application No. 0 615 777describes a method and an appertaining device in which urea is suppliedfrom a storage vessel or reservoir, using a precision dosing unit, to acarrier air stream. The precision dosing unit works according to theprinciple of a feeding screw, a change in dosing being achieved via achange in the rotary speed of the feeding screw. The solid urea iseither already present in powder form in the storage vessel or, ifbigger particles are being used, is conveyed to a millwork before beingtransported. In order to prevent the absorption of moisture, it issuggested there that one should pack the urea under the exclusion ofhumidity of the air, and to open the package only after inserting itinto the storage vessel.

The use of loads of urea that are packed in an air-tight manner may bevery expensive, since the urea first has to be packed in an air-tightmanner, excluding moisture. In addition, the individual packages mustnot be too large, since in the course of time the urea absorbs moisture,even in the storage vessel, because of its hygroscopic properties.However, smaller urea portions call for frequent refilling of thestorage vessel, which is of little convenience to the user of a motorvehicle.

In order to overcome these aspects, German Published Patent ApplicationNo. 197 54 135 describes carrying the urea along in a solid monolithicstructure. Depending on requirements, using a removing device, theappropriate quantity of urea is continuously removed from a block, ifnecessary, the urea is finely ground if the particles are still too big,and the powdery urea is then fed to a carrier gas stream for transport.The removing device is a rotating disk or roll fitted with bristles,abrasive grains, knives or milling tools. By changing the advancingspeed of the removing device with respect to the urea block, the dosingquantity may be varied.

Using this procedure, the problem of baking together of the particles issolved, however, other problems remain. Thus, the prepreparation of theurea to form monolithic blocks may be necessary, which means acorresponding preliminary expenditure. An additional disadvantage comesabout due to the use of the removing device described there. Duringremoval from the urea block, unavoidably urea particles of differentsizes may be produced. This has the result that the urea quantitysupplied to the system varies as a function of the particles. Exactdosing in accordance with instantaneous requirements, if at allpossible, may be done only within wide boundaries.

German Published Patent Application No. 197 54 135 describes using anadditional millwork by which the particles removed from the urea blockare milled down to a powder. This, however, may have the disadvantagethat the conversion of the urea block to powdered urea represents anadditional preinserted method step which may negatively influence thereaction time of the overall system, that is, the system may become tooinert. Because of that, the requirement for ammonia conditioned upon theload change may not be able to be satisfied in the short run, or, in theshort run, an oversupply may be created.

SUMMARY

Based on this background, example embodiments of the present inventionmay provide a method and a device for dosing and transporting dry urea,which may permit exact dosing of the urea within wide ranges ofquantities in a greatly dynamic manner. Reliable transport of the ureato the processing location may also be achieved.

Example embodiments of the present invention are described below.

An example embodiment of the present invention is based on the use ofurea, for carrying out the SCR method, in a form that is alreadyavailable in large quantities. Thus, urea is applied in large volume toagriculturally used areas, e.g., for fertilization. The urea from thefertilizer industry corresponds in its composition, form and dimensionsto the requirements hereof, e.g., it is available in the dry state inspherical or sphere-like shape. Such urea is also designated by thetechnical term pellet. However, within the present context, the termpellet is not limited to a spherical or sphere-like shape, which onlyrepresents an exemplary form in which the urea is used. Rather, the termpellet used herein includes, in general, grainy material which might bebroken up just as well.

As a result of the mass production in large industrial plants foragricultural use, such urea may be available in large quantities asstarting material, and may therefore be extremely cost-effective. Anysize is basically possible as the setpoint size for the individualpellets. However, as the size of the pellets decreases, a finergradation for dosing may be achieved. If the dimensions of the pelletsotherwise used for fertilizing differs too greatly from the setpointvalue hereof, simply passing the pellets through a screen may yield asuitable size fraction. An example size fraction includes pellets havingdeviations from the setpoint size in the range of about 5%. The setpointsize may have a diameter of, e.g., 1 to 3 mm.

However, it should be understood that example embodiments of the presentinvention are not limited to using urea in pellet form, but include, adevice in which it is possible to supply these pellets from a storagevessel in a predefined dosing to the conversion process to ammonia. Thistakes place by isolating the pellets and subsequently passing them on toa carrier air stream, which performs the further transport. In thismanner of proceeding, therefore, the smallest possible dosable unitquantity is determined by a pellet. By sequential isolation andsubsequent transport of the pellets, a transport flow is produced inwhich the speed of the isolation and of the transport may be decisivefor the dosing.

According to an example embodiment of the present invention, theisolation and supplying of the pellets to the carrier air stream maytake place with the aid of a disk, ringwheel or a hollow cylindersection which has a plurality of receiving elements. By the rotation ofthe disk, ring wheel or the hollow cylinder section, the receivingelements are alternately brought into a position for filling and aposition for blowing out. The rotational movement of the disk, ringwheel or the hollow cylinder section may be performed in a simple mannerby a rotary drive, such as an electric motor. The change in dosing maytake place, in this context, in a simple manner, by changing the rotaryspeed. This manner of proceeding may make possible a greatly dynamicsituation by rotary speed changes, and may also be very simple andreliable. The direct influence of the rotary speed change on the dosingmay lead to very short reaction times of the overall system.

An alternative to the disk shape or to the ring shape or to the hollowcylinder section is a slide-shaped portioning element that executes ato-and-fro swinging motion. Besides motor drives, whose rotationalmotion has to be converted to linear motion, a swinging electromagnetmay also be possible as the drive.

In order to ensure that the pellets are supplied individually and oneafter the other to the carrier air stream, the receiving elements may beadjusted to the shape and the dimensions of the pellets such, in eachcase, only one pellet will fit into them.

For blowing out the pellets, according to an example embodiment of thepresent invention, the cross section of the blow-out opening may beformed to be larger than the receiving element, which may make blowingout the pellet easier.

An example embodiment of the present invention may provide that thetransport line, in which a carrier air stream for transporting thepellets is produced, has a slightly bigger cross section than themaximum size of the pellets would require. In this manner, whentransporting the pellets, the “blow-pipe” effect may be advantageous,e.g., in the transport tubing, the pellets form a kind of displaceableplug which almost completely fills the cross section of the transporttubing and thus closes it. The carrier air acting upstream generates anoverpressure in the transport line which is the cause of the transportof the pellet in the transport line. This kind of transport may providethat bridge building by the material to be transported may be excluded.Furthermore, there may be no hovering of the material in the carrier airstream, since the carrier air stream pushes the pellet ahead of itselflike an air cushion. In this manner one may successfully route thetransport line both uphill and downhill in narrow windings withoutexperiencing interferences or fluctuations in the dosing of the pellets.

In an example embodiment of the present invention, a portioning elementmay be partially covered by a baffle. In this context, the baffle takeson a scraper function and may thereby prevent jamming and squeezing thepellets during the isolation procedure. Additionally, the compressed airnozzle for the carrier air stream may be integrated into the baffle, sothat the baffle takes care at the same time of sealing the carrier airstream to the inside of the container.

In an example embodiment of the present invention, as many receivingelements as possible may be provided on a circumferential line of theportioning element. This may provide that, for dosing, a slightrotational speed of the portioning element may be sufficient, andtherefore filling the receiving elements may be managed with greatcertainty. The possible number of receiving elements may be determinedby the radial distance of the receiving elements from the rotationalaxis and the mutual clearance from one another. The minimum mutualclearance of the receiving elements, according to an example embodimentof the present invention, may be greater than the diameter of thecompressed air nozzle, so that one achieves that in each case only onereceiving element has air pressure applied to it. It is also possible toselect the clearance to be slightly smaller, so that, independently ofthe setting of the portioning element, a carrier air stream constantlyprevails in the transport line.

An example embodiment of the present invention may provide forming theclearance of the receiving elements from one another greater than thediameter of the compressed air nozzle, and at the same time continuouslyto introduce air into the transport line at a location downstream fromthe compressed air nozzle. For this, for example, a part of thecompressed air stream may be conducted upstream from the compressed airnozzle in a bypass line to the transport line. This may make certainthat the pellets are blown out one after another from the receivingelements, and at the same time that there may take place a continuouscarrying off in the carrier air stream. Thereby the efficiency and theoperating safety of the device herein may be increased.

The pressure prevailing in the transport system may exceed theenvironmental pressure at the output location of the pellets from thetransport line. This may provide that no air from the outside may getinto the dosing device and the transport device, with which there may beconnected the danger that moisture could penetrate the system from theoutside. In the case of operating standstill, i.e., when the engine isshut down, a blocking element may additionally be present that takesover the function of air-tight cutting off from external influences.

The transport of the urea using an air stream or gas stream may providethat the urea is cooled during its transport and is protected frommoisture. If necessary, only dry air is used for the carrier air stream,which is, for example generated in an air conditioning compressor.

Since, in the course of time, clogging of the receiving elements may notbe completely excluded, according to an example embodiment, a cleaningmechanism for the receiving elements may be provided. The cleaningmechanism has one or more cleaning pins which, in the course of themovement of the portioning element, penetrate the just-emptied receivingelements, and in this context, push possibly remaining pellets or pelletremains from the receiving element. In this context, the cleaning pinsmay be located either supported at shiftable lengths and driven via acam lobe on a shaft, or they may be located on a cleaning wheeluniformly distributed on the circumference and having a radialalignment.

Example embodiments of the present invention are described in greaterdetail below with reference to the appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a dosing and transporting device accordingto an example embodiment of the present invention for carrying out theSCR method.

FIG. 2 is a perspective view of the storage vessel having the dosingdevice illustrated in FIG. 1.

FIG. 3 is a vertical cross-sectional view through the bottom part of thestorage vessel having the dosing and transporting device, taken alongline III-III illustrated in FIG. 4.

FIG. 4 is a horizontal cross-sectional view through the apparatusillustrated in FIG. 3 taken along the line IV-IV illustrated in FIG. 3.

FIG. 5 is a perspective view of an example embodiment of the dosingdevice having an integrated cleaning mechanism.

DETAILED DESCRIPTION

FIGS. 1 and 2 schematically illustrate equipment for dosing andtransporting dry urea for carrying out the SCR method. The equipmentincludes a storage vessel 1, which is used to store a large number ofurea pellets 2. Storage vessel 1 has a cylindrical section in its upperpart, which narrows, downwardly, in the shape of a funnel. At the lowestpoint on storage vessel 1, dosing device 3 is arranged. Dosing device 3will be explained in greater detail with respect to FIGS. 3 and 4.Finally, on the lower side of dosing device 3 there is a motor 4 as thedrive for dosing device 3.

Transporting pellets 2 from storage vessel 1 is done with the aid of acompressed air source 5, such as in the form of an air compressor, whichis connected to dosing device 3 via pressure line 6. An additionalpressure line 7, for transporting pellets 2, connects dosing device 3with a reactor 8, in which the conversion of urea pellets 2 to ammoniatakes place, due to the effect of heat. The generated ammonia isintroduced via line 9 into the exhaust gas stream of an internalcombustion engine.

FIGS. 3 and 4 illustrate dosing device 3 with parts of the transportingdevice. First is seen the lower, funnel-shaped part of storage vessel 1,which ends in a cylindrical extension 10. Cylindrical extension 10surrounds, in a force- or non-positive-locking and gas-tight manner,dosing device 3, which forms the bottom of storage vessel 1.

Dosing device 3 has a circular disk 11, which closes flush with thelower edge of cylindrical extension 10. At its circle center aconcentric circular opening 12 is provided. Axis of rotation 13 extendsthrough the center, and perpendicular to the plane of circular disk 11.Eccentrically, approximately between the center and the edge of circulardisk 11, a bore 14 goes through the disk element, with its axis parallelto axis of rotation 13.

Towards the inside of storage vessel 1, adjoining to circular disk 11,there is a plane-parallel and coaxially arranged portioning disk 15which has at its lower side, facing circular disk 11, an extension 16 inthe form of a short cylindrical piece, that extends from the middle ofthe lower side. Portioning disk 15 is located with extension 16 inopening 12, while maintaining a minimal play. In this context, circulardisk 11 forms a sliding bearing for portioning disk 15, on which it issupported rotatably about axis of rotation 13.

Portioning disk 15 has a large number of parallel axis bores, whichextend from the upper side of portioning disk 15 to its lower side, andwhich are situated uniformly distributed along a common circumferentialline. Each of the bores forms a receiving element 17 for one pellet 2 ineach case. The radial distance of receiving elements 17 from the axis ofrotation 13 is equal to the radial distance of bore 14 from the centerof circular disk 11, so that by turning portioning disk 15, receivingelements 17 may be brought one after another into a position alignedwith bore 14.

Above portioning disk 15, a roughly ring-shaped baffle 18 is seen, thatis also plane-parallel, which keeps such a great distance from circulardisk 11 that portioning disk 15 is able to rotate within this space. Theouter edge of baffle 18 adjoins the inner wall of cylindrical extension10, and the inner edge, over the greatest part of its circumference,traces a concentric circle which, in axial projection, overlaps with theouter edge of portioning disk 15. In this context, however, receivingelements 17 remain freely accessible from the inside of vessel 1. Onlyin the area of bore 14 is baffle 18 enlarged segmentally, so that bore14 is covered in a planar manner in portioning disk 15.

In the direction of axis of symmetry 19, there extends, both throughextension 10 of storage vessel 1 and through baffle 18, a radial bore20, which ends above bore 14 of portioning disk 15. Perpendicular tobore 20, an additional bore 21, that is parallel to axis of rotation 13,has been introduced into baffle 18, that is aligned with bore 14 incircular disk 11, and which forms a continuous channel with bore 20. Inthis manner, baffle 18 is used together with bores 20 and 21 to form acompressed air nozzle.

Pressure line 6, coming from pressure source 5, is connected to thisbore 20. The compressed air stream is marked by arrow 22. Pressure line7 is connected to bore 14 in circular disk 11, and it leads to reactor 8(FIG. 1). The carrier air stream prevailing in pressure line 7 is markedby arrow 23.

The drive required for the rotation of portioning disk 15 is taken careof by a rotary speed-controlled electric motor 4, which is fastened tothe lower side of circular disk 11, directly below opening 12, and whosedrive shaft 24 penetrates in a form- or positive-locking manner intoshort cylindrical piece extension 16. The direction of rotation ofportioning disk 15 is indicated by arrow 25.

During the operation of the motor vehicle, in order to carry out the SCRmethod, a certain quantity of ammonia is supplied to the exhaust gasstream, as a function of the respective load state of the internalcombustion engine. According to an example embodiment of the presentinvention, the quantity of ammonia required is brought about byconversion of urea pellets 2 in reactor 8. In this context, in orderconstantly to supply reactor 8 with a sufficient quantity of urea,pellets 2 are supplied from a storage vessel 1, in the quantity that isrequired at any particular moment.

To do this, it may first be necessary to isolate pellets 2 that arepresent in bulk in storage vessel 1. Because of the force of gravity,lowest pellets 2 lie, making contact, on the upper side of portioningdisk 15 that is surrounded by baffle 18 and is freely accessible. Theisolation of the pellets takes place in that pellets 2 reach receivingelements 17 of portioning disk 15 as a result of their gravity. Thisprocess takes place along with the continuing rotation of portioningdisk 15, in each case only one pellet 2 reaching receiving elements 17,as a result of the size of receiving elements 17. From here on, thepellets located in receiving elements 17 are marked 2′. The maximumspeed of rotation of portioning disk 15 is limited because pellets 2require a minimum of time to occupy receiving elements 17.

During the course of rotation of portioning disk 15, receiving elements17 filled with pellets 2′ are one after the other brought into aposition in which their upper side lies opposite compressed air nozzle18, 20, 21, and their lower side is aligned with bore 14. Sincecompressed air is applied to compressed air nozzle 18, 20, 21, pellets2′, upon reaching this position, are blown out of receiving element 17,and get into transport line 7. At this stage, the pellets are marked 2″.

By the continuing rotation of portioning element 15, a receiving element17, that has been blown out and is therefore empty, after passingthrough the region covered by baffle 18, arrives again at storage vessel1 to be filled, while another receiving element 17, occupied by a pellet2′ is taken to compressed air nozzle 18, 20, 21, where the blowing outof next urea 2′ takes place.

The individual receiving elements 17 in portioning disk 15 are separatedby crosspiece regions of predetermined width. During the rotation,receiving elements 17 and crosspiece regions are alternatingly passed bycompressed air nozzle 18, 20, 21, the crosspiece regions having theeffect of interrupting compressed air stream 22. In this manner there iscreated an intermittent carrier air stream 23. By positioning there abypass line, which connects pressure line 6 to transport line 7, anintermittent compressed air surge may be generated at the exit of nozzle18, 20, 21, with continuous transport of pellets 2″ in transport line 7.

This type of isolation has the effect that pellets 2′ reach transportline 7 in a sequence in time, which leads to a spatial clearance ofpellets 2″ in transport line 7. By the adjustment of the internaldiameter of transport line 7 to the dimensions of pellets 2, aircushions form in transport line 7 between two subsequent pellets 2″which are separated and limited by individual pellets 2″, and betweenwhich, with respect to each other, no considerable air exchange takesplace. One speaks here of a “blow-pipe effect”, which may ensure thaturea pellets 2″ in transport line 7 maintain a predetermined clearanceand do not bump into one another, which may subsequently cause bridgebuilding and clogging. The size of the air cushion gives the clearancebetween two pellets 2″ in line 7, and is a function of the air quantitythat gets from receiving elements 17 to transport line 7 during andbetween the blowing out of two subsequent pellets. The air cushions pushpellets 2″ ahead of themselves, independently of the course of transportline 7, even any desired differences in height and curve radii beingmanaged, until pellets 2″ are finally fed into reactor 8.

The change in dosing of the urea is made via a rotary speed change ofportioning disk 15. By increasing the rotational speed, pellets 2′ getinto transport line in a shorter sequence in time. By contrast, if therotational speed is slowed down, a reduction in dosing may be achieved.In this manner, for example, without any problem, a dosing of 0 pelletsper second to 40 pellets per second is possible, which is equal to amass flow of 0 g per hour to approximately 600 g per hour. Since arotary speed change of driving motor 4, and thus of portioning disk 15,leads directly to a change in dosing, an adaptation of the quantity ofurea to changing load states of the internal combustion engine may bemade very accurately and with great dynamism.

Since it may not be completely excluded that receiving elements 17become partially or completely clogged in the course of time withpellets 2 or pellet remains, according to an example embodiment of thepresent invention, dosing device 3 is outfitted with a cleaningmechanism 26, which is postconnected to compressed air nozzle 18, 20, 21in the direction of motion of portioning element 15, and which will beexplained in more detail with reference to FIG. 5.

Because of greater clarity, FIG. 5 illustrates only dosing device 3,without storage vessel 1, pressure lines 6 and 7 and drive motor 4. Onemay see portioning disk 15, having receiving elements 17, situatedrotatably about axis of rotation 13, between circular disk 11 and baffle18. From the lower side of portioning disk 15 there extends, centrally,short cylindrically shaped extension 16, which penetrates into opening12 of circular disk 11. Short cylindrically shaped extension 16 issurrounded concentrically by a toothed rim 32, which is connectedfixedly to the lower side of portioning disk 15, and which forms a partof an angle drive.

The other part of the angle drive includes drive shaft 27, which issupported, freely rotatable, in circular disk 11, below portioning disk15, perpendicular to axis of rotation 13. At the inner end of driveshaft 27 there is a frustum-shaped pinion 28, whose teeth engage withtoothed rim 32. In addition, on drive shaft 27, affixed withforce-locking, there is a cleaning wheel 29 that is provided uniformlyover its circumference with radially aligned cleaning pins 30. Toaccommodate drive shaft 27, pinion 28 and cleaning wheel 29, acorresponding hollow space is formed in circular disk 11 which iscontinued to the lower side of circular disk 11, and which forms anopening 31 there.

The arrangement of cleaning mechanism 26 within dosing device 3 is suchthat, with respect to the rotational movement 25 of receiving elements17 it is postconnected to compressed air nozzle 18, 20, 21, and that thedistance of cleaning wheel 29 from portioning disk 15 makes possible thepenetration of receiving elements 17 by cleaning pins 30.

During the operation, described before, of the device according to anexample embodiment of the present invention, the rotational movement 25of portioning disk 15, initiated by drive motor 4 via toothed rim 32, istransmitted to pinion 28 and further on to drive shaft 27 and cleaningwheel 29. Consequently, rotational motion 25 of portioning disk 15 runssynchronously with rotational motion 33 of cleaning wheel 29 having thecleaning pins situated on it. By the suitable arrangement of cleaningpins 30 on cleaning wheel 29, in this context, in each case a cleaningpin 30 engages with a receiving element 17, and possibly lifts pellets2′ or pellet remains that may be present out of receiving element 17.Urea particles that appear in this context, because of gravity, fallthrough opening 31 and out of dosing device 3. In this manner it may bepermanently ensured that there are always available empty receivingelements 17 for the isolation and dosing of pellets 2 that are locatedin storage vessel 1.

1-36. (canceled)
 37. A device for dosing and transporting dry urea,comprising: a storage vessel adapted to store dry urea in the form ofpellets, a wall of the storage vessel having an opening to which atransport line is connected from outside; a compressed air nozzlearranged inside the storage vessel at a distance from the opening andaligned with the opening; and a portioning element having an upper sidepointing to the inside of the storage vessel and a lower side arrangedopposite to the wall of the storage vessel, at least one continuouschannel having a cross-section greater than dimensions of the pelletsconnecting the upper side and the lower side arranged to form at leastone receiving element for the pellets, the portioning element movablysupported between the compressed air nozzle and the wall of the storagevessel to alternatingly be brought from one position in which thereceiving elements are freely accessible from the upper side of theportioning element into a position in which the receiving elements arearranged in an aligned manner between the compressed air nozzle and theopening.
 38. The device according to claim 37, wherein the device isadapted to perform an SCR method in a motor vehicle.
 39. The deviceaccording to claim 37, wherein the portioning element includes one of(a) a disk, (b) an annular disk and (c) a hollow cylinder sectionsupported rotatable between the compressed air nozzle and the wall ofthe storage vessel.
 40. The device according to claim 39, wherein theportioning element includes a plurality of one of (a) axially parallelreceiving elements and (b) radial receiving elements arranged on onecircumferential line and having a same clearance between one another.41. The device according to claim 39, wherein the receiving elements arearranged at a radial distance from an axis of rotation.
 42. The deviceaccording to claim 39, wherein a speed of rotation of portioning elementis variable to set and change the dosing.
 43. The device according toclaim 37, wherein the portioning element includes a slide movable backand forth along a linear guideway.
 44. The device according to claim 43,wherein the receiving elements are arranged parallel to a direction ofmotion of the slide.
 45. The device according to claim 43, wherein theslide is driven electromagnetically.
 46. The device according to claim37, wherein the pellets have a setpoint size one of (a) in diameter and(b) diagonally of 1 to 5 mm.
 47. The device according to claim 37,wherein the pellets have a setpoint size one of (a) in diameter and (b)diagonally of 2 to 3 mm.
 48. The device according to claim 37, whereinthe pellets have a setpoint size one of (a) in diameter and (b)diagonally of 1.9 mm.
 49. The device according to claim 46, whereindeviations of the pellets from the setpoint size are less than 10%. 50.The device according to claim 46, wherein deviations of the pellets fromthe setpoint size are less than 5%.
 51. The device according to claim37, wherein the receiving elements have a depth and cross-sectionadapted to accommodate a pellet.
 52. The device according to claim 37,wherein the receiving elements have a minimum mutual clearance greaterthan an exit diameter of the compressed air nozzle.
 53. The deviceaccording to claim 37, wherein the transport line includes a connectionto an introduction of compressed air.
 54. The device according to claim37, wherein a compressed air line upstream of the compressed air nozzleand the transport line downstream of the compressed air nozzle areconnected by a bypass line.
 55. The device according to claim 37,wherein the receiving elements have a minimum mutual clearance that issmaller than an exit diameter of the compressed air nozzle.
 56. Thedevice according to claim 37, wherein the opening in the wall of thevessel has a cross-section that is at least a same size as across-section of the receiving elements.
 57. The device according toclaim 37, wherein the opening in the wall of the vessel has across-section that is greater than a cross-section of the receivingelements.
 58. The device according to claim 37, wherein the transportline has an unobstructed cross-section that is larger than a maximumdimension of the pellets.
 59. The device according to claim 37, whereinupper side edges of the portioning element are covered by a baffle. 60.The device according to claim 59, wherein the compressed air nozzle isintegrated into the baffle.
 61. The device according to claim 37,wherein pressure in the transport line is greater than environmentalpressure.
 62. The device according to claim 37, wherein pressure in thetransport line is greater than environmental pressure by 0.1 to 1.0 bar.63. The device according to claim 37, wherein pressure in the transportline is greater than environmental pressure by at least 0.5 bar.
 64. Thedevice according to claim 37, further comprising a cleaning unitpostconnected to the compressed air nozzle and adapted to free thereceiving elements from urea remains.
 65. The device according to claim64, wherein the cleaning unit includes at least one cleaning pin adaptedto penetrate through the receiving elements.
 66. The device according toclaim 65, wherein the cleaning pin is supported and activatedtransversely to a plane of the portioning element in a longitudinallyshiftable manner.
 67. The device according to claim 65, wherein thecleaning pin is arranged in radial alignment about a drive shaft thatextends parallel to a plane of the portioning element and transverselyto a direction of motion of the receiving elements, the cleaning pinadapted to penetrate through the receiving elements during rotation. 68.The device according to claim 65, wherein motion of the cleaning pin iscoupled to motion of the portioning elements.
 69. The device accordingto claim 67, wherein the portioning element is connected to the driveshaft via an angle drive.
 70. A method for dosing and transporting dryurea from a storage vessel to a processing location, the urea present inthe form of pellets, comprising: isolating the pellets; and transferringthe pellets to a carrier air stream.
 71. The method according to claim70, wherein the isolating is performed with a portioning element havingat least one receiving element, each receiving element adapted toreceive one pellet.
 72. The method according to claim 71, wherein thetransferring includes bringing up the receiving element to a compressedair nozzle and blowing the pellet out from the receiving element. 73.The method according to claim 71, further comprising at least one of (a)regulating a speed of motion of the portioning element and (b)regulating a speed of the carrier air stream.
 74. The method accordingto claim 70, wherein a constant carrier air stream is present in atransport line.
 75. The method according to claim 72, further comprisingintroducing compressed air into a transport line downstream from thecompressed air nozzle.
 76. The method according to claim 75, wherein thecompressed air introduced into the transport line is taken from upstreamof the compressed air nozzle.
 77. The method according to claim 76,wherein pressure in the transport line is greater than environmentalpressure at an end of the transport line.
 78. The method according toclaim 76, wherein pressure in the transport line is greater by 0.1 to1.0 bar than environmental pressure at an end of the transport line. 79.The method according to claim 76, wherein pressure in the transport lineis greater by at least 0.5 bar than environmental pressure at an end ofthe transport line.
 80. The method according to claim 71, furthercomprising blowing out the receiving elements by an intermittentcompressed air stream.
 81. The method according to claim 71, furthercomprising cleaning the receiving elements after blowing out thereceiving elements.